exterior paint bubble

[Newby2]

My house is a mock Tudor, and the exterior wall of the front face of the house (between the black wooden beams) is painted white. I had it re-painted three years ago. Recently I have found that there are a number of areas where the paint has unsightly blistering (bubbles). Is it because the paint that the contractor used three years ago is not up to the standard, or is it quite common given the fact that the paint has been exposed to the elements?

Any advice would be much appreciated.

 

[joe-90]

It's probably due to poor quality substrate (crumbly render) or could be water getting underneath somewhere.